Correct; Jötun Owl Keeper has a blue mana symbol in its rules text, so it can't be included in a Commander deck whose commander's color identity is white only (C.R. 903.4, 207.1). This is so even though the cumulative upkeep cost here can be paid with just W.
In general, wherever a colored mana symbol appears in a card, whether in a cost or otherwise, that symbol will count toward that card's color identity (review C.R. 903.4). (One exception is reminder text; for example Basilica Guards's color identity is white only, even though (W/B) appears in its reminder text [C.R. 903.4c, 207.2a].)
Even though it's a mono white card - producing mono white owls it has a blue symbol as a possibility in it's upkeep cost.
In general, wherever a colored mana symbol appears in a card, whether in a cost or otherwise, that symbol will count toward that card's color identity (review C.R. 903.4). (One exception is reminder text; for example Basilica Guards's color identity is white only, even though (W/B) appears in its reminder text [C.R. 903.4c, 207.2a].)
See also this thread and this thread.
EDIT (Apr. 5, 2021): One rule was renumbered in the meantime.